By Hiroki Akamatsu

We are developing the Frequency Domain Multiplexing (FDM) read-out of Transition-Edge Sensors (TESs) for future astronomical projects. TESs are ultra-sensitive thermistors working at low-temperature (~100 mK) which can provide unprecedented resolving power (E/dE, dE: Energy resolution, E: incident energy). To realize 1000's pixel TESs array, signal multiplexing technology is one of the critical components. In the FDM scheme, TESs are coupled to a passive LC-resonator and biased with alternating current (AC bias) at MHz frequencies. For the X-ray Integral Field Unit (X-IFU) instrument onboard Athena, a multiplexing factor of 34 pixels/channel is required.

Using high-quality factor LC filters, low-noise two-stage SQUID amps developed by VTT and, TES calorimeters developed at SRON, we have successfully demonstrated a 37-pixel simultaneous readout with a summed energy resolution of 2.23 eV at 5.9 keV for the first time. The measured performance meets the specification of the X-IFU instrument. The impact of the multiplexing on the performance was estimated to be 0.9 eV in quadrature, thus adding only little to the basic TES detector noise. The origins of the degradation have been identified and the solutions being implemented into the system.

Access to the manuscript in ADS.